The beneficial growth promoting effects of antimicrobials in animal feed to minimise disease have been known since the 1940s. However, the Swann report (1969) requested a more strict government control on the use of antibiotics in feed. Since the Swann report, there has been increasing concern about the transmission of resistant bacteria and this has resulted in the EU ban on antibiotic growth promoters taking effect from the 1 Jan. 2006. This ban on antibiotic growth promoters will unquestionably affect disease control on farms as well as animal performance and necessitates effective alternatives. The removal of antibiotics from animal feed will also lead to an increase in the proportions of harmful microbes like E. coli and Salmonella in the gut microflora of farm animals.
Even in the current scenario, the number of cases of food poisoning in developed countries like Ireland has increased over the last decade with Campylobacter spp. infection being the most common and Salmonella spp. infection the second most common cause of illness. New salmonella control measures are being introduced to Ireland and these control measures will cause serious difficulties for some animal, cattle, poultry and pig producers.
Current intensive farming techniques have also lead to an increase in stress related disorders in farm animals, including poor gut health and a high incidence of diseases like PMWS. Weaning constitutes one of the most stressful situations in the life of the pig (Melin et al., 2004). The young pig is subjected to a myriad of stressors (Pluske et al., 1997) which leads to impaired immune function and an increased susceptibility towards infections (Hiss et al., 2003). The use of infeed antibiotics has reduced these problems due to a reduction in the microbial population within the gastrointestinal tract, as well as a change from pathogenic towards beneficial bacteria. This results in better nutrient absorption, less substrate for the proliferation of pathogenic organisms and an improvement in the health status and integrity of the gastrointestinal tract (Close, 2000). However, as a result of various public health scares associated with animal product consumption there is increasing consumer pressure to reduce the use of antibiotics (Williams et al, 2001). There therefore exists an urgent need to find alternatives to in-feed antibiotics that can give the above mentioned benefits, without adversely affecting human health.
Given the cost pressures in intensive farming, animal performance, particularly at early stages of growth, are of crucial importance to the farmer. In this regard, the key parameters to be considered include the average daily gain (weight gain per piglet per day), the feed conversion ratio (a measure of the performance efficiency of the piglet), the average daily intake (grams of food intake/day) and a reduction in scouring (a measure of the consistency of the feces, and an indicator of diarrhea in the young pig). Any composition that seeks to improve performance should effect an increase in the ADG, an improvement in the FCR (as indicated by a reduction in its value) and a reduction in scouring (indicated by more solid feces).
Similarly, unhealthy eating habits in humans have had a huge impact on gut health. In a recent survey of European manufacturers (Leatherhead R.A Survey), 21% said that gut health would have the greatest influence on the functional food market. Thus, there exists a need for a composition that can improve the gut health of humans and act as a prebiotic for beneficial bacteria.
Replacement of antimicrobials: There are a number of alternative strategies that are available as replacement products for in-feed antibiotics and salmonella control, including diet acidification, inclusion of various probiotics into the diet, fructo-oligosaccharides, enzymes and herbs.
Dietary acidification using organic acids is the most common strategy currently being used. This is believed to have an important function improving digestion and assisting the microbial balance in the intestinal tract. The beneficial effects of these vary according to type, the strongest acid being formic acid. A low pH is required to activate critical digestive enzymes in the stomach of the pig. Also one of the greatest barriers to the invasion of the intestinal tract by pathogenic bacteria is acidic pH. However, acids have limited use unless they are protected in the stomach as otherwise they are likely to be neutralized by the enzymes in the upper digestive tract. Furthermore, as the pig grows, its ability to naturally produce sufficient acid for digestion increases thus reducing the benefit of an acidifier. Thus, acids are useful additives only in the diet of small pigs and pigs fed low quality diets.
Also, where high density diets high in ingredients derived from milk have been used the response to acid addition has been much less. This is because the lactose in milk is converted to lactic acid creating desirable changes in the gastric environment, thus reducing the need for additional acidification. However, lactose is an expensive dietary component, and there exists a need to discover components that can limit the amount of lactose required in the diet, while enhancing its beneficial effects. Furthermore, high levels of lactose make diets difficult to prepare, as lactose is hygroscopic and difficult to deal with, especially at high levels.
Another common strategy being used is the introduction of probiotics (or direct-fed microbials) in animal diets. However, the development of probiotics is limited by certain restraining factors including stringent European legislation on the use of probiotics and a wide range of alternate ingredients. Furthermore, animal feed products are often treated at high temperatures and probiotics (being microbial in nature) cannot survive such temperatures.
Fructose oligosaccharides (FOS), prebiotics currently being sold in the pig market, have several advantages. However, some researchers (Jaskari et al, 1998) have questioned the selectivity of FOS as a substrate for beneficial carbohydrate bacteria. In in-vitro trials, they have been found to increase the growth of all bacteria (including bactericides found naturally in the gut as well as E. coli), thus raising doubts over their selectivity. Thus FOS may in themselves, not be an ideal solution.
None of these strategies match antimicrobials in terms of performance and all give very variable results. There therefore exists a need to provide a food supplement that can act as an alternative to antibiotics and improve animal performance.
Impact of unhealthy diets in humans: There has been an increased tendency in recent years to increase the levels of protein in human diets. This tendency is exacerbated by the existence of high protein diets, like the Atkins diet, that increase the levels of protein in the diet while reducing the levels of carbohydrates. Such diets have a profound influence on the gut microflora and increase the levels of protein fermenting bacteria like E. coli and Salmonella, while reducing the levels of beneficial carbohydrate fermenting bacteria like the lactobacilli and the bifidobacteria (Lynch et al unpublished) Therefore, there exists a need for compositions that can restore the balance of microflora in the gut and can boost the incidence of beneficial bacteria. The key strategy being followed currently is the use of probiotics, which are particular strains of microbes fed directly to the individual. However, the human gut flora consists of over 400 species of bacteria and probiotics can only aim to re-introduce a few of these species. Current prebiotics, like insulin are non-specific and may in fact boost the levels of harmful bacteria like E. coli (Jaskari et al, 1998, Pierce at al, 2005), while increasing the levels of beneficial bacteria like bifidobacteria. Therefore, there exists a need for a prebiotic composition that can selectively boost the levels of beneficial carbodydrate fermenting bacteria like the bifidobacteria while reducing the levels of E. coli and Salmonella. 